Automatic arc welding machines

ABSTRACT

Device for performing completely automatic welding operations using fusible or infusible electrode, in accordance with a program directly governed by the path of the electrode, by emission of electric signals corresponding to equal elementary portions of path, such signals being collected by at least one step-by-step motor actuating the programmer. The device is characterized by the fact that the programmer includes means of controlling and adjusting all the welding parameters listed below : welding current strength, current pulsations, wire advance, wire advance pulsations, starting and stopping the unwinding of the wire, the rate of movement of the electrode, variations in such rate, arc fading, the minimum flow of protective gas, adjustment of the position of a torch perpendicularly to the welding wire and parallel to the surfaces to be welded, adjustment of the distance of the torch from the surfaces to be welded, slope of the torch in a plane passing through the welding wire, and slope of the torch in a plane perpendicular to the welding wire. The programmer turns step-by-step under the impulse of the electric signals emitted by the means of moving the torch, so that the angular speed of the programmer is directly proportional to the path travelled by the torch.

United States Patent 1 Paulange 1 June 5,1973

[54] AUTOMATIC ARC WELDING MACHINES [76] Inventor: Serge Paulange, l2,Raute de Verton, Nantes 44, France [22] Filed: Oct. 6, 1971 [21] Appl.No.: 186,960

[30] Foreign Application Priority Data Nelson Ross et al.

..2l9/60 A ..2l9/60 A Primary Examiner-J. V. Truhe Attorney-Raymond A.Robic [57] ABSTRACT Device for performing completely automatic weldingoperations using fusible or infusible electrode, in accordance with aprogram directly governed by the path of the electrode, by emission ofelectric signals corresponding to equal elementary portions of path,such signals being collected by at least one step-bystep motor actuatingthe programmer, The device is characterized by the fact that theprogrammer in cludes means of controlling and adjusting all the weldingparameters listed below welding current strength, current pulsations,wire advance, wire advance pulsations, starting and stopping theunwinding of the wire, the rate of movement of the electrode, variationsin such rate, are fading, the minimum flow of protective gas, adjustmentof the position of a torch perpendicularly to the welding wire andparallel to the surfaces to be welded, adjustment of the distance ofthe. torch from the surfaces to be welded, slope of the torch in a planepassing through the welding wire, and slope of the torch in a planeperpendicular to the welding wire. The programmer turns step-by-stepunder the impulse of the electric signals emitted by the means of movingthe torch, so that the angular speed of the programmer is directlyproportional to the path travelled by the torch. I

14 Claims, 11 DrawingFigures PATENTEDJJN .1

SHEET 2 OF 4 PATENTED JUN 5 75 SHEET 3 [1F 4 AUTOMATIC ARC WELDINGMACHINES This invention relates to automatic arc welding machineswherein the operating cycle is prescribed and constantly controlled as afunction of the advance of the tool (hereinafter called torch) bearingthe infusible electrode and the filler metal wire, or possibly thefusible wire conducting the welding current, depending on the methodselected.

More specifically, it is intended to improve the completely automaticand controlled performance of all the adjustments to the parametersgoverning a weld, even when the latter has to include peculiarities suchas adjusting the puslations during fusion or sloping the torch, oradjusting the length of the arc or the rate of unwinding of the fusiblewire.

This invention uses the method of programming based on impulses emittedby a device which transforms equal portions of path travelled by thetorchholder, i.e. by the electrode, into electric signals. In otherswords, specific values of the welding parameters, according to thewelding cycle previously selected, correspond to any position of thetorch along its path. Consequently, the number of impulses isindependent of the speed of the torch. It is solely a function of thewelding path. According to the invention, the improved programmer doesnot only deal with the said parameters which it has already beenpossible to programme and control, i.e. the flow of protective gas, therate of advance of the torch, the strength and voltage of the weldingcurrent and possibly the corrective action of accessories on startingand stopping; it also includes some or all of those which it has not upto now been possible to programme. Thus, the slope of the torchis takeninto account and, consequently, the distance of the electrode (fusibleor infusible) from the part to be welded. There is also the movement ofthe torch in a direction parallel to the surfaces to be welded andperpendicular to the welding rod. There is also the rate of unwinding ofthe filler metal wire. Up to now this rate has been a function of thewelding current strength, for a given section of welding rod. And aboveall there are those which characterize the most recent methods of arcwelding and which can only be adjusted and controlled within theframework of a programmed cycle; these are the welding current puslationor the pulsated advance (or unwinding) of the tiller metal wire or thepulsation of these two latter factors.

Various methods of obtaining impulses representing elementary portionsof the torchs travel along its path are already known. The said impulsesare electric signals provided either by a simple mechanical contactsystem, or a magnetic system, or by an optical system, all these systemsbeing synchronised with the motor moving the torch. These electricsignals generally actuate impulse counters or step-by-step motors whichuse cams to control the various parameters usually corrected byprogramming (i.e. advance, current strength and voltage, timing whenstarting and stopping, gas flow). This known principle, following acontinuous or sequential cycle, although limited up to now to theadjustable factors mentioned above, has given distinctly improvedresults over other methods. Unfortunately, the time taken to make a weldand the quality of the weld, regardless of the difficulties, arebecoming more and more important. Some operations are still manual, orat least independent of programming. This is the case with theadjustment of the distance of the torch from the part. Knownimprovements have nevertheless been made to correct the distance betweenthe part and the electrode-holder. They make the length of the arcconstant despite irregularities in the surfaces of the parts to bewelded. In this way the torch is mounted on a flexible support kept incontact with the said parts by a knurled wheel rolling or sliding on thelatter. Some makers have even mounted the torch on a mechanised or jacksystem, moving perpendicularly to the surfaces to be welded. But theseimprovements are aimed at independent adjustment which does not comewithin the framework of a programmed operation. Moreover, to date,.nocycle has, as a function of the welding torch path, applied a variationto the slope of the latter (electrode or filler metal or both) inrelation to the part to be welded, as some awkward surfaces sometimesdemand. Whatever the direction of slope, it is often necessaryconsequently to correct the distance-of the electrode from the part tobe welded. This manual operation is tricky and wastes time.

Welding on heavy thicknesses of sheets, for example, often requiresseveral passes in the V-shaped groove formed by the chamfers. Thesepasses are superimposed, but the path of the electrode is not the sameevery time, The slope of the torch may also be different. Up to now, theposition of the torch perpendicularly to its normal path, possibly itsslope and consequently its height in relation to the surfaces to bewelded, have not been corrected automatically at each pass as a functionof the size of the groove formed by the chamfers.

Present and recent are welding methods with filler metal tendincreasingly to use a pulsated current, as has been the case for a longtime with welds made with an infusible electrode. That is to say, thefusion current, as from a basic value, is subjected to rapid controlledvariations. This method allows considerable local temperature increases,without excessively heating the parts to be welded as a whole, and atthe same time gives better penetration by the welding material. Theduration of maximum current production may be different from that ofminimum current production. The duration of minimum current is itselfadjustable. The said current values (maximum and minimum) can alsodiffer according to the type of weld. These parameters are at presentprescribed by prior manual settings. But it has not yet been possible toprogramme automatically the variation thereof as a function of a givenwelding path. This lack raises problems with complicated welds, e.g. inoperations with an automatic, orbital welding head (rotation of the toolaround a circular part, in a vertical plane) or with all repetitivewelds. Pulsating the advance of the wire to obtain the same penetrationeffects or combining current pulsations with wire advance come upagainst the same difficulties.

As mentioned above, the known programmer controls the parameters(strength, torch speed, gas flow, timing at the beginning and end of thepath) by means of ordinary cams. At the end of each sequence (e.g.orbital welding on a tube), a quick return to zero device allows thenext sequence to be started. This arrangement has disadvantages when thenumber of parameters to be controlled is high and it is necessary tocorrect them from one pass to the next. The improvements are alsodirected at this lack.

The method in accordance with the invention and the device derivingtherefrom enable the above-mentioned disadvantages to be avoided. Theymake it possible to perform better quality, more complicated anddifficult welds, repetitive or otherwise, without defects. This re sultis obtained by means of automatically adjusting all the factorsmentioned above which go to make the weld, while previously, only someof these factors could be programmed. Thus, awakward surfaces, round orotherwise, can be welded automatically and the groove formed by chamfersin thick sheets can be filled with several passes, etc. In grooves whosewidth increases towards the top surface, it is possible e.g. to make aweld on one face of the said groove, then on the other at the next passand so on, the extent of the torchs transversal movement increasing inaccordance with the width of the said groove.

Moreover, it means that the method of arc welding by pulsated current orby advancing a pulsated fusible wire, or by pulsating these twotogether, can be used in accordance with a pre-established programme andis thus not subject to error by the operator. In fact, the associationof the device which detects the position of the torch on its path, andthe device which obtains pulsated fusion allows a continuous orsequential cycle to be programmed. This cycle, of course, takes intoaccount foreseeable welding difficulties during the torchs travel. Thepermanent or intermittent combining of the pulsated current and pulsatedwire advance method can in any case hardly be expected to give goodresults except within the framework of a programmed cycle. This methodis just as applicable to welds with a tungsten infusible electrode andordinary filler metal wire as possibly to welds with fusible wire alsoused as an electrode. In all cases, the weld deforms the parts less bypenentrating deeper for the same rod width. The molten bath is bettermaintained. The performance and life of the electrodes are improved inthe case of welding with a tungsten electrode.

It should be noted that even when the pulsations become useless,adjustment of the rate of unwinding of the fusible wire can be obtainedautomatically as a function of the advance of the torch-holder on itsprescribed path, irrespective of the number of other adjustment factorsincluded in the programme. Combined with a device emitting a pulsatedcurrent or with a device which gives pulsated unwinding of the fusiblewire, or with these two devices, it naturally gives full scope forprogramming all or some of the other characteristic welding factors fromthe path of the torch (impulses): gas flow, average welding currentvalues, rate of advance of the torch-holder, average wire unwindingspeed, slope of the torch in all directions, its distance from the partsto be welded, its position in a plane perpendicular to the path of thetool. Finally, in an orbital automatic welding operation (e.g. on tubes)several passes can be made, i.e. several revolutions with the samesystem of special cams, improving the continuity and the chance tocorrect certain parameters during one or several of the said passes,without having recourse to the rapid return to zero process.

The device covered by this invention comprises two separate parts. Thefirst includes the means needed to transform signals emittedequidistantly along the path of the tool, which transformation enableseach parameter to be adjusted by means of step-by-step motors and camspositioned characteristically, the first unit being called a programmer.

The said parameters controlled by the programmer, taken as a whole or inpart, include: current strwngth, torch speed, current pulsations, wireadvance, wire advance pulsations, the time when the wire is started orstopped, arc fading characteristics, temporary variations in torch speedfrom the basic programme, the gas flow.

The second part, essential to an understanding of the invention,includes the whole of the movements and the means enabling the torch towork automatically during the operation, in accordance with theinstructions transmitted by the programmer cams. The programmer receivesthe instructions from the system driving the torch-holder along the pathto be travelled by the electrode and this path, whether it is repetitiveor not, is imaginarily cut up into equal elementary por tions. Duringeach of the latter, an electric signal is emitted. The angular movementof the programmer cams is thus in direct ratio to the movement of thetorch. It is the said cams which control the abovementioned parameters.

A good understanding of the invention will be obtained from thefollowing description and from the attached drawings. This descriptionis only given as a non-limiting example. It relates to an automaticwelding head known as the orbital type, i.e. the torch is driven by asupport which revolves around a round body, e.g. a tube. In thedrawings,

FIG. 1 is an overall frontal view of the welding head, showing the meansand movements for dimensional adjustment;

FIG. 2 is a left-hand view of the head of FIG. 1 along a line AA showingthe means of sloping the torch;

FIG. 3 is a frontal part view of a preferred variation with the torchbearing an infusible electrode and a separate filler metal wire;

FIG. 4 is a frontal part view of a variation with the spool of wiremounted directly on the mobile toolholder plate;

FIG. 5 is a sectional view of a weld on a thick sheet with severalpasses;

FIG. 6 is a diagrammatic view of the components which make up theprogrammer which receives the electric signals;

FIG. 7 is a view of the mounting of one of the cams (in at least twoparts) in the programmer;

FIG. 8 is a profile view of the cam shown in FIG. 7;

FIG. 9 is a diagram (welding current strength as a function of time)relating to the pulsated current;

FIG. 10 is another diagram relating to the pulsated current with othercharacteristic values, and

FIG. 11 is a diagrammatic frontal view of an orbital welding head withU-shaped crown and support, and impulse emitter on one of the drivingpinions.

As showin in FIG. 1, the means for adjusting the torch in relation tothe parts to be welded are mounted on a crown 1 revolving around a part,such as e.g. the tube 2, on which one or several welding passes are tobe made automatically. This welding head, which is drawndiagrammatically, will be described later in this text, as an example.It is articulated, with 4 of freedom, on the crown l, itself driven by atoothed rack and pinion system 3, the said pinion (with fixed axis)being driven by a variable speed motor (e.g. direct current) 4. Thelatter also drives a multiplier actuation a pinion 5, so that theangular speed ratios of parts 5 and l have a selected value n. Thepinion 5 is fitted with a finger 6 closing a contact 7 at eachrevolution. It is evident that the contact 7 will thus emit n electricsignals during the full rotation of the supporting crown 1, which cutsthe path of the torch 8 around the tube 2 into n equal imaginaryportions (one per electric signal) during the first complete cycle (from0, start of the weld, to 0' end of the first cycle). The number n may beas high as may berequird by the accuracy of the adjustment of thewelding parameters, such as e.g. 100 or 1,000.

The means of creating electric signals may be different. For example,flashes of light actuating a photoelectirc cell or a magnetic bodypassing in front of a contact with a flexible lamina, which are meansalready in current use.

FIG. 6 shows the use of the electric signals emitted by contact 7, thenfiltered and shaped by any means 9 (electronic components) and finallyreceived by a stepby-step motor 10 (or a motor which works by impulses,

each of the latter making it turn a specific fraction of Y1 arevolution). The said motor 10 is mounted in a unit 11 called theprogrammer housed in the same cabinet in a fixed position outside thewelding head, but close to the working position. With a suitablyselected reduction device 12 it drives an initial set of cams shown insection in accordance with their diameter in FIG. 6. The cam 13 fixesthe programme for the welding current strength value during the travel.The roller device 14' actuates an electronic device ,15, selected fromamong known systems, which precisely and accurately varies the speed ofthe direct current motor 4 driving the crown 1. The cam 16 acts on thewelding current strength by means of the roller device 17 and adjustingcomponents 18 and 18a. The latter are selected from known types enablingthe said current to be adjusted, controlled and varied as a function ofthe parameters affecting it, notably voltage. The cams l3 and 16 maymake a revolution or a fraction of a revolution when the crownzl makes acomplete rotation, corresponding inthe example selected to a weldingcycle. They may also make one revolution for several cycles, when e.g.

it is necessary to make several superimposed passes. To,

achieve these various possibilities, either the reduction ratios can bechanged (at 12 or at 5 a reduction which may moreover be variedgradually, or the number of signals recorded or received can bemodified. The stepby -step motor 10 also drives a second set of cams,possibly by means of a suitably selected reduction device 19. Severalcams whose functions are defined below aremounted on the same shaft 20.The cam 21 relates to the fusible wire. It controls the moment when thesaid wire. begins its advance, then governs its speed, variable orotherwise, according to the thickness of the deposit, then controls itsstoppage. Starting and stopping can, of course, be gradual. The wire isfed by a direct current motor 22 (FIG. 1) with a known system of knurleddriving wheels. The cam 23 controls certain speed changes in the motor 4driving the corwn 1. It serves,'e.g. and possibly, to correct theadvance of the torch, especially at the start and finish of the cycle,complementing the main cam 13. The cam 24 serves to control the fadingof the arc at the end of the operation, i.e. gradually to weaken thecurrent by the addition of resistances, complementing the cam 16. Thecam 25 controls, at a certain time, the cessation of current regulationduring fading. The latter can easily be controlled in the welding methodcomprising an infusible electrode and a filler metal wire. The samedoesnot apply to the fusible electrode wire method.-The earns 26, 27, 28, 29adjust the various parameters-(1,4. D,.d)

of the pulsated current from a minimum-value i (FIG.

10) fixed by cam 16, or from a maximum value I (FIG. 9) fixed by thesame cam. In other words, a complementary potentiometer comes or isshunted into the circuit for a specific time D, when the saidpotentiometer is added and d, when it is removed. This occurs inaccordance with a certain rhythm which can very in a'ccordance with theform of graph (strength/time see FIG. 9 and 10, as an example) which hisdesired to obtain. The production of these impulses, i.e. fixing themoments when the potentioneter(s) enter into or leave the electriccircuit, is achieved by any adjustable means 30 such as a time-switch orother devices with electronic components. Of course, the said cams donot act directly on the current, but via a contact or a set of contactsin 30. At a given time, via relays, they thus being into play componentscontained in 30 which modify the values of the pulsation parameters inaccordance with a known process. It is therefore possible separately toadjust the value v of the amplitudes and the times D (high strength) andd (low strength). It is also possible to control the start and the endof the pulsations, which explains the four cams provided for thisoperation, which cams may in some cases be reduced to a lesser number byassociating certain parameters in the electronic relay device 30. As anexample, the values of D and d are about 0.1 to 1 second, in normaloperations. The cams 31 and 32 control the impulses advancing thefusible wire; they act by micro-contact on a device 320 which interruptsthe rotation of the motor 22 (complementing the orders given by the cam21) for a certain time and in accordance with an adjustable rhythm,which parameters are synchronised with the current pulsations. When thepulsations are solely produced by the wire or solely by the current, thecorresponding superfluous instructions are cancelled either electrically(opening contacts and relays) or mechanically (by e.g. lifting thecontacts on the cams). A single cam may replace 31 and 32, if the systemof synchronisation with the pulsated current control so allows. The cam33 is designed to vary the flow of protective gas or at least the limitof the safety flow (by any known means)..The other earns 34, 35, 36, 37,control the movements of the torch 8, i.e. respectively:

its movement parallel to a generatrix on the tube 2 (by the motor 38 onthe welding head in FIG. 1),

its distance from the surfaces to be welded, i.e. its distance from thetube 2 (by the motor 39),

its slope in a plane-perpendicularto the axis of the tube 2 (by themotor 40), and

its slope in a plane passing through one axis of the tube 2 (by themotor 41).

These two latter degrees of freedom, governed by the path of the torch,via the cams 36 and 37, enable successive deposits to be made atdifferent slants in the groove formed by chamfers on thick parts 2a(FIG. 5). It is clear that the path is not the same on each cycle, noris the slope of the torch. In this case, the cam 34 also be used to movethe unit supporting the torch parallel to a generatrix. Heightcorrection by the cam 35 is usually essential.

Taking as an example the lining of the groove formed by the chamfers 2band 20, it can be seen that at the end of each cycle the torch can beshifted (with or without slope), a shift the width of which is afunction of the size of the groove (2b 20), every time a deposit hasjust been made. This automatic variation of the width can be provided bycams 34 35 36 37 combined. But it can also more easily be obtained, insimple cases, by a single other cam which we shall call 34a which, atthe end of each cycle, modifies thewidth in accordance with a givenprogramme. This result is obtained either by increasing the pace of oneor several of the motors 38 39 40 41 at each cycle change. It can alsobe obtained by step contacts successively put into service or shunted sothat the travel of the intermediate support(s) in question is increasedafter each pass (or cycle).

Each cam mounted on the shaft 20 actuates one or several micro-contactssuch as 42 and 43, as shown in FIG. 7. The said contacts can be situatedon several levels, in order at a given moment to cause the opening orclosing of a circuit which modifies (or corrects) the value of theparameter corresponding to the said cam. As is already evident from theforegoing, the modification can be made via the means appropriate to theparameter. To give non-limiting examples: a potentiometer, motorised orotherwise; an electronic device for varying the speed of the directcurrent motor, a simple contact relay for starting a synchronous motorfor a time prescribed by the cam, previously set timeswitches, etc.

In order to be able to programme a welding operation accurately, eachcam is made up of two or several discs,

shaft 20 by means of quick-fastening nuts, which locking is effectedafter orienting the said discs in relation to one another. In this way,a large number of combinations can be obtained to meet the requirementsof the programme. The said cams mounted on the shaft 20 are notnecessarily all used, as the welding operation may be more or lesscomplicated. The shaft 20 can be synchronised with the cams l3 and 16when the weld only comprises one cycle. But it can also turn twice orthree times and so on faster if the operation is carried out in 2 cyclesor 3 cycles and so on when each cycle has the same characteristics. Ifthe cycles differ substantially from one'another, it is preferable forthe shaft 20 to be at the same speed as the cams 13 and 16. The latterare not all-or-nothing acting on the strength and on the rate of advanceof the torch. Their profiles are such that they define directly thevalue of these two basic parameters for each angular position of thesaid cams.

As already mentioned above, the reduction devices 12 and 19 which drivethe sets of cams can be variable and therefore adjustable, either bymeans of pinions,

sliding as in a gearbox or by gradual ratio systems such as a disc and asliding friction wheel.

In order for the welding head to be able to respond to the programmeorders, the various articulations holding the torch and bearing on thecrown l have to be motorised. This aspect emerges from the descriptiongiven below of the said head. Generally, the motors are direct current,variable speed motors. In some cases, they can be step-by-step motorsreceiving secondary impulses emitted on basis of the instructions fromthe corresponding cam. The said head (FIG. I) is, e.g. de-

signed for welding with a fusible electrode, the wire 8:: passing insidethe torch 8. The motor 22 pushes the said wire by means of the pinionsand wheels such as 22a. The body 8b of the torch receives the protectivegases and possible cooling fluid. The wire is wotind on a spool 80.

The crown 1 bears a right-angle bracket 47 on which the part 49 slides,in a slide 48. This movement is effected parallel to the axis ofrevolution of the tool, by means of the motor 38 actuating a rack andpinion system. Another part 50 (vertical slide 51) bearing an arm 52,slides on the part 49. The end of the arm 52 holds a roller 58 bearingconstantly on the tube 2 to be welded, held there by a spring 52 thetension of which can be adjusted by the milled knob 54 and the screw 55.The motor 39 turns the nut 56 which moves the screw 57 along its axis,which screw is integral with the roller 58 fixed in rotation. Thedimension J can thus be otal movement is approximately a point situatedon the electrode 8a. It is produced by the motor 41, via a pinion(mountedon 52a) and a toothed segment integral with the part 59.Finally, the torch support 64*slid'es on the latter pivotally. Thecentre of the rotary movement is also situated approximately on theelectrode 8a, by means of an aperture shaped like the arc of a circle65, in which the studs 66 and 67'screwed into the support 64 engage,locking being possible by means of the knob 68. The motor 40 drives(pinion-toothed segment) the support 64.

These two latter articulations (64 in relation; to 59 and 59 in relationto 52a) can also be obtained by means of an axle in a bore, still with arack and pinion,

if the rotation of the part does not need to have the electrode as itscentre. The movements will then be less accurate.

FIG. 3 shows a partial view of a head with an infus'ible electrode 69,held and cooled by the torch 8d. The fusible wire 70 carried by thespool 71 unwinds by means of the same motor 22 actuating knurled wheels,as before. The support proper of the torch 64a is articulated, like thesupport 64, by means of the motor 40 (with rack andpinion). Theremainder of the head is .the same as before.

In accordance with a variation, the spool of fusible wire can be mounteddirectly on the crown l, as shown in FIG. 4. The wire 8a is thensupported by as many rollers as necessary in order to maintain asuitable ra- I dius of curvature. The support 64 is thereby simplified.

lt is shown with an axle of articulation instead of an aperture shapedlike the arc of a circle, as an example. The same applies to a weldinghead with infusible electrode and filler metal.

FIG. 11 shows that the mobile crown 1 can be open in the shape of aletter U, as may the support 72 for the said crown, which support isfixed on the tube 2 to be welded. The crown bearing the torch 8d withwire 70 and the various articulations thereof described above slidespivotally on the support 72, concentrically to the latter. The flexiblepiping and cables feeding the torch roll around columns fixed on thesupport 72. The opening in the parts 1 and 72 is such that they can befitted roundtthe said tube, when they are in concordance. When the crownl is driven by the pinions (or tangent screw) 73 and 74, strictlysynchronised, at least one of the latter is always engaged, even whenthe opening is opposite the other. One of the pinions 74, for example,drives the finger 6 through the multiplier 5, as explained at thebeginning of the description; the said finger 6 via the contact 7 emitsimpulses to the programmer.

It goes without saying, and indeed is obvious from the foregoing, thatthe invention is not confined to the examples described above. On thecontrary, it includes all possible variations, provided they are notoutside the scope of the claims.

This invention is used for complicated welds calling for completeautomation. Thus, it is eminently suitable for repetitive parts whichrequire high-class welds. It is mainly applied to orbital welds, i.e.where the tool rotates around a round part for welding. But it can alsobe used for welds on any other kind of flat or awkward surface. There isalso a use for it in operations other than welding; polishing, cuttingup and even some kinds of repetitive machine-finishing.

I claim:

1. Automatic welding apparatus for welding, for example, two tubes endto end in a continuous welding operation comprising:

a. a single welding head supporting a welding torch;

b. a crown supporting said welding head and mounted for rotation in thesame direction of rotation around at least one full circumference of thetube to be welded;

c. means for driving said crown;

d. means for generating welding current pulsations;

e. means for generating wire advance pulsations;

f. means for mounting said welding head on said crown for movement ofthe torch parallel to the axis of the tube to be welded;

g. means for mounting said welding head on the crown so as to permitvariations of the distance of the welding torch from the surface to bewelded;

h. means for mounting said welding head on said crown for permittingvariations of the angle of the torch in a plane perpendicular to thewelding seam; means for mounting said welding head on the crown forpermitting variations of the angle of the torch in a plane parallel tothe welding seam; j. means responsive to rotation of said crown forgencrating electric pulses corresponding to equal elementary portions ofthe path of said torch;

k. a step-by-step motor energized by said electric pulses; l

l. a programmer mounted outside the said welding head and including ashaft driven by said step-bystep motor and upon which are mounted aseries of cams, said cams being adapted to control said welding currentpulsations, said wire advance pulsations, said movement of the torchparallel to the axis of the tube to be welded, said variations of thedistance of the welding torch from the surface of the tube to be welded,said variations of the angle of the torch in a plane perpendicular tothe welding seam, and said variations of the angle of the torch in aplane parallel to the welding seam.

2. Automatic welding apparatus as defined in claim comprise a fingeroperated by said crown through reducing gears so as to generate pluralelectric pulses during each revolution of the crown in order to permitsaid cams to continuously control the welding parameters at any momentof the welding operation.

3. Automatic welding apparatus as defined in claim 2, wherein the shaftsupporting the cams is coupled to the motor through a reduction deviceso as to cause said cams to rotate less than 360 in order to permit eachcam to control its associated parameters for the full welding operationeven if such welding operation lasts for several revolutions of thetorch around the tube to be welded.

4. Automatic welding apparatus as defined in claim 1, wherein additionalcams are provided for controlling the following parameters: the averagewelding current strength, the flow of protective gas, and the speed ofrotation of the welding head.

5. An automatic welding apparatus as defined in claim 1, wherein eachcam is madeof several'discs which may be oriented one with respect tothe other and locked laterally together on the shaft by means of quickfastening nuts so as to permit to obtain a large number of combinationsof profiles for controlling the welding parameters.

6. An automatic welding apparatus as defined in claim 1, wherein themeans for varying the position of the torch parallel to the axis of thetube comprises a bracket secured to said crown, an horizontal slideadapted to slide on said bracket, and a motor mounted on said bracketand adapted to move said slide by means of a rack and pinion systemunder the control of its associated cam.

7. An automatic welding apparatus as defined in claim 6, furthercomprising a vertical slide secured to said horizontal slide, an armsecured to said vertical slide, a shaft threaded into the end of saidarm, a roller 1, wherein said means for generating electric pulsessecured to the end of said shaft and bearing against the tube to bewelded, and a motor for rotating said shaft under the control of itsassociated cam.

8. An automatic welding apparatus as defined in claim 7, wherein themeans for varying the angle of the torch in a plane perpendicular to thewelding seam comprises a rib secured to said vertical slide and havingan aperture therein in the shape of an arc of a circle, and a rightangle part provided with two studs in one of its right angle portionsand sliding in said aperture so that the center of pivotal movement is apoint situated on the end of the torch contacting the tube to be of acircle, a support for said welding head provided with studs sliding insaid aperture so that the center of pivotal movement is a point situatedon the end of the torch contacting the tube to be welded, and a motormounted on said right angle part and moving said support through a rackand pinion system under the control of its associated cam.

10. An automatic welding apparatus as defined in claim 4, wherein themeans for generating welding current pulsations comprises a first camcontrollingthe average value of the current strength, second and thirdcams operating suitable potentiometers so as to modulate said averagecurrent strength in order to determine the maximum and minimum values ofthe pulsated current, and fourth and fifth cams controlling the lengthof time during which said potentiometers are operated.

11. An automatic welding apparatus as defined in claim 1, wherein saidmeans for generating wire advance pulsations comprises a wire feedingmotor associated with said welding head, an electronic control devicefor controlling the operation of said motor, a first cam operating saidelectronic control device for controlling the average speed of saidmotor, and a second cam operating on said electronic control device forperiodically interrupting the rotation of the motor.

12. An automatic welding apparatus as defined in claim 11, wherein thecurrent pulsations are synchronized with the wire advance pulsations.

13. An automatic welding apparatus as defined in claim 1, wherein saidcrown has a U-shaped cross section, and wherein said means for drivingsaid crown comprises a support of U-shaped cross section overlappingsaid crown and fixed on the tube to be welded, said support carryinggears coupled with said crown and a motor for rotating said gears.

14. Automatic welding apparatus as defined in claim 13, furthercomprising columns secured to said support for permitting winding offlexible pipings and cables feeding the torch from said programmer, thuspermitting to wind such pipings and cables plural turns around thesupport when the welding operation requires plural revolutions aroundthe tube to be welded.

1. Automatic welding apparatus for welding, for example, two tubes endto end in a continuous welding operation comprising: a. a single weldinghead supporting a welding torch; b. a crown supporting said welding headand mounted for rotation in the same direction of rotation around atleast one full circumference of the tube to be welded; c. means fordriving said crown; d. means for generating welding current pulsations;e. means for generating wire advance pulsations; f. means for mountingsaid welding head on said crown for movement of the torch parallel tothe axis of the tube to be welded; g. means for mounting said weldinghead on the crown so as to permit variations of the distance of thewelding torch from the surface to be welded; h. means for mounting saidwelding head on said crown for permitting variations of the angle of thetorch in a plane perpendicular to the welding seam; i. means formounting said welding head on the crown for permitting variations of theangle of the torch in a plane parallel to the welding seam; j. meansresponsive to rotation of said crown for generating electric pulsescorresponding to equal elementary portions of the path of said torch; k.a step-by-step motor energized by said electric pulses; l. a programmermounted outside the said welding head and including a shaft driven bysaid step-by-step motor and upon which are mounted a series of cams,said cams being adapted to control said welding current pulsations, saidwire advance pulsations, said movement of the torch parallel to the axisof the tube to be welded, said variations of the distance of the weldingtorch from the surface of the tube to be welded, said variations of theangle of the torch in a plane perpendicular to the welding seam, andsaid variations of the angle of the torch in a plane parallel to thewelding seam.
 2. Automatic welding apparatus as defined in claim 1,wherein said means for generating electric pulses comprise a fingeroperated by said crown through reducing gears so as to generate pluralelectric pulses during each revolution of the crown in order to permitsaid cams to continuously control the welding parameters at any momentof the welding operation.
 3. Automatic welding apparatus as defined inclaim 2, wherein the shaft supporting the cams is coupled to the motorthrough a reduction device so as to cause said cams to rotate less than360* in order to permit each cam to control its associated parametersfor the full welding operation even if such welding operation lasts forseveral revolutions of the torch around the tube to be welded. 4.Automatic welding apparatus as defined in claim 1, wherein additionalcams are provided for controlling the following parameters: the averagewelding current strength, the flow of protective gas, and the speed ofrotation of the welding head.
 5. An automatic welding apparatus asdefined in claim 1, wherein each cam is made of several discs which maybe oriented one with respect to the other and locked laterally togetheron the shaft by means of quick fastening nuts so as to permit to obtaina large number of combinations of profiles for controlling the weldingparameters.
 6. An automatic welding apparatus as defined in claim 1,wherein the means for varying the position of the torch parallel to theaxis of the tube comprises a bracket secured to said crown, anhorizontal slide adapted to slide on said bracket, and a motor mountedon said bracket and adapted to move said slide by means of a rack andpinion system under the control of its associated cam.
 7. An automaticwelding apparatus as defined in claim 6, further comprising a verticalslide secured to said horizontal slide, an arm secured to said verticalslide, a shaft threaded into the end of said arm, a roller secured tothe end of said shaft and bearing against the tube to be welded, and amotor for rotating said shaft under the control of its associated cam.8. An automatic welding apparatus as defined in claim 7, wherein themeans for varying the angle of the torch in a plane perpendicular to thewelding seam comprises a rib secured to said vertical slide and havingan aperture therein in the shape of an arc of a circle, and a rightangle part provided with two studs in one of its right angle portionsand sliding in said aperture so that the center of pivotal movement is apoint situated on the end of the torch contacting the tube to be welded,and a motor for pivoting said right angle portion through a rack andpinion system under the control of its associated cam.
 9. An automaticwelding apparatus as defined in claim 8, wherein the means for varyingthe angle of the torch in a plane parallel to the welding seam comprisesthe other portion of said right angle part which is also provided withan aperture therein in the shape of an arc of a circle, a support forsaid welding head provided with studs sliding in said aperture so thatthe center of pivotal movement is a point situated on the end of thetorch contacting the tube to be welded, and a motor mounted on saidright angle part and moving said support through a rack and pinionsystem under the control of its associated cam.
 10. An automatic weldingapparatus as defined in claim 4, wherein the means for generatingwelding current pulsations comprises a first cam controlling the averagevalue of the current strength, second and third cams operating suitablepotentiometers so as to modulate said average current strength in orderto determine the maximum and minimum values of the pulsated current, andfourth and fifth cams controlling the length of time during which saidpotentiometers are operated.
 11. An automatic welding apparatus asdefined in claim 1, wherein said means for generating wire advancepulsations comprises a wire feeding motor associated with said weldinghead, an electronic control device for controlling the operation of saidmotor, a first cam operating said electronic control device forcontrolling the average speed of said motor, and a second cam operatingon said electronic control device for periodically interrupting therotation of the motor.
 12. An automatic welding apparatus as defined inclaim 11, wherein the current pulsations are synchronized with the wireadvance pulsations.
 13. An automatic welding apparatus as defined inclaim 1, wherein said crown has a U-shaped cross section, and whereinsaid means for driving said crown comprises a support of U-shaped crosssection overlapping said crown and fixed on the tube to be welded, saidsupport carrying gears coupled with said crown and a motor for rotatingsaid gears.
 14. Automatic welding apparatus as defined in claim 13,further comprising columns secured to said support for permittingwinding of flexible pipings and cables feeding the torch from saidprogrammer, thus permitting to wind such pipings and cables plural turnsaround the support when the welding operation requires pluralrevolutions around the tube to be welded.